Structure and function of the AAA+ protein CbbX, a red-type Rubisco activase

Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyses the fixation of atmospheric CO(2) in photosynthesis, but tends to form inactive complexes with its substrate ribulose 1,5-bisphosphate (RuBP). In plants, Rubisco is reactivated by the AAA(+) (ATPases associated with various cellular activities) protein Rubisco activase (Rca), but no such protein is known for the Rubisco of red algae. Here we identify the protein CbbX as an activase of red-type Rubisco. The 3.0-? crystal structure of unassembled CbbX from Rhodobacter sphaeroides revealed an AAA(+) protein architecture. Electron microscopy and biochemical analysis showed that ATP and RuBP must bind to convert CbbX into functionally active, hexameric rings. The CbbX ATPase is strongly stimulated by RuBP and Rubisco. Mutational analysis suggests that CbbX functions by transiently pulling the carboxy-terminal peptide of the Rubisco large subunit into the hexamer pore, resulting in the release of the inhibitory RuBP. Understanding Rubisco activation may facilitate efforts to improve CO(2) uptake and biomass production by photosynthetic organisms.     

Structure of a methyl-coenzyme M reductase from Black Sea mats that oxidize methane anaerobically

The anaerobic oxidation of methane (AOM) with sulphate, an area currently generating great interest in microbiology, is accomplished by consortia of methanotrophic archaea (ANME) and sulphate-reducing bacteria. The enzyme activating methane in methanotrophic archaea has tentatively been identified as a homologue of methyl-coenzyme M reductase (MCR) that catalyses the methane-forming step in methanogenic archaea. Here we report an X-ray structure of the 280?kDa heterohexameric ANME-1 MCR complex. It was crystallized uniquely from a protein ensemble purified from consortia of microorganisms collected with a submersible from a Black Sea mat catalysing AOM with sulphate. Crystals grown from the heterogeneous sample diffract to 2.1?? resolution and consist of a single ANME-1 MCR population, demonstrating the strong selective power of crystallization. The structure revealed ANME-1 MCR in complex with coenzyme M and coenzyme B, indicating the same substrates for MCR from methanotrophic and methanogenic archaea. Differences between the highly similar structures of ANME-1 MCR and methanogenic MCR include a F(430) modification, a cysteine-rich patch and an altered post-translational amino acid modification pattern, which may tune the enzymes for their functions in different biological contexts.     

Über den Zusammenhang der Carnotschen Theorie mit der Thermodynamik

Ohne Zusammenfassung Vorgelegt von M. Klein     

Distinct t(7;9)(q34;q32) breakpoints in healthy individuals and individuals with T-ALL

After V(D)J-mediated translocations, signal joints are retained on one of the derivative chromosomes. We report here that such signal joints are highly reactive and constitute unstable genomic elements with potential oncogenic properties.     

Quantum jumps of light recording the birth and death of a photon in a cavity

A microscopic quantum system under continuous observation exhibits at random times sudden jumps between its states. The detection of this quantum feature requires a quantum non-demolition (QND) measurement repeated many times during the system's evolution. Whereas quantum jumps of trapped massive particles (electrons, ions or molecules) have been observed, this has proved more challenging for light quanta. Standard photodetectors absorb light and are thus unable to detect the same photon twice. It is therefore necessary to use a transparent counter that can 'see' photons without destroying them. Moreover, the light needs to be stored for durations much longer than the QND detection time. Here we report an experiment in which we fulfil these challenging conditions and observe quantum jumps in the photon number. Microwave photons are stored in a superconducting cavity for times up to half a second, and are repeatedly probed by a stream of non-absorbing atoms. An atom interferometer measures the atomic dipole phase shift induced by the non-resonant cavity field, so that the final atom state reveals directly the presence of a single photon in the cavity. Sequences of hundreds of atoms, highly correlated in the same state, are interrupted by sudden state switchings. These telegraphic signals record the birth, life and death of individual photons. Applying a similar QND procedure to mesoscopic fields with tens of photons should open new perspectives for the exploration of the quantum-to-classical boundary.     

Unexpected complexity of the Wnt gene family in a sea anemone

The Wnt gene family encodes secreted signalling molecules that control cell fate in animal development and human diseases. Despite its significance, the evolution of this metazoan-specific protein family is unclear. In vertebrates, twelve Wnt subfamilies were defined, of which only six have counterparts in Ecdysozoa (for example, Drosophila and Caenorhabditis). Here, we report the isolation of twelve Wnt genes from the sea anemone Nematostella vectensis, a species representing the basal group within cnidarians. Cnidarians are diploblastic animals and the sister-group to bilaterian metazoans. Phylogenetic analyses of N. vectensis Wnt genes reveal a thus far unpredicted ancestral diversity within the Wnt family. Cnidarians and bilaterians have at least eleven of the twelve known Wnt gene subfamilies in common; five subfamilies appear to be lost in the protostome lineage. Expression patterns of Wnt genes during N. vectensis embryogenesis indicate distinct roles of Wnts in gastrulation, resulting in serial overlapping expression domains along the primary axis of the planula larva. This unexpectedly complex inventory of Wnt family signalling factors evolved in early multi-cellular animals about 650 million years (Myr) ago, predating the Cambrian explosion by at least 100 Myr (refs 5, 8). It emphasizes the crucial function of Wnt genes in the diversification of eumetazoan body plans.